1. Field of the Invention
The invention concerns a circuit arrangement for the actuation of an electric motor main drive which is operated from a frequency converter with a controlled bridge circuit in a large domestic appliance which is also equipped with an auxiliary drive.
2. Discussion of the Prior Art
In order to be able to adjust a rotary field which rotates independently of the fixed mains frequency and the mains voltage, for the operation of synchronous motors and asynchronous motors, it is usual to employ a circuit arrangement of the general kind set forth in large domestic appliances, in particular; for example, for actuation of the drive motor for the washing drum in a washing machine or the circulating pump for the dishwashing agent circuit in a dishwashing machine, as the main drives thereof. In that situation the field coil of the respective motor is operated from the mains rectifier with a dc voltage intermediate circuit connected downstream thereof, by way of a frequency converter half-bridge arrangement which can be switched over in multiple mode. Rotary field control as a consequence of co-ordinate actuation of the switches in respect of repetition frequency, duration and mutual phase position is usually effected from a microprocessor in accordance with a program which is predetermined in accordance with the motor characteristic and on which present items of control and regulating information are superimposed in accordance with an operating program which is currently to be executed.
Besides such a main drive, a large domestic appliance is usually to be found to have an auxiliary drive of lower power, for additional functions which are only temporarily required, such as for example for filling or emptying the working chamber with an uninfluenced delivery, which for cost reasons is usually operated directly from the single-phase mains, without expensive rectifier control systems. This therefore involves accepting the fact that the mode of operation of the auxiliary drive cannot be optimized.